Lipids: Nature’s Flavor Enhancers

Chapter 10

Chemical Structure of Lipids

• The Glycerides:• Monoglycerides• Diglycerides• Triglycerides

• Phospholipids• Sterols

Lipids are a category of organic compounds that are insoluble in water and have a greasy feel. There are three types of lipids with unique chemical structures:

The Glycerides

The core of lipids is the glycerol molecule.

Molecules that have a glycerol base are called glycerides.

The Glycerides Fatty Acids are

organic molecules that consist of a carbon chain with a carboxyl group at one end.

A carboxyl group is a carbon atom, two oxygen atoms, and a hydrogen atom.

The carboxyl group of a fatty acid will readily react with a hydroxyl group of glycerol.

MonoglycerideOne

fatty acid attached

at the site of a hydroxyl group.

DiglycerideA glycerol with two

fatty acids attached

at the site of a

hydroxyl group.

TriglycerideA glycerol

with a fatty acid attached at each of the three hydroxyl

sites.

Major type of fat found in

foods and in the body.

Triglycerides

• Can have 3 different fatty acids attached

• 20 fatty acids to choose from• Create different characteristics• Cooking performance• Shelf life• Nutritional value

Phospholipids

Is a glycerol base with 2 fatty acids and a phosphorus-containing acid attached.

The fatty acids are soluble in fats. The phosphorus-containing acid is

soluble in water. Allows to mix w/both water-based and

fat-based substances. Phospholipids help fats stay mixed in

water-based solutions Keep foods like mayonnaise from separating.

Sterols

Are complicated molecules derived or made from lipids.

They include: Cholesterol (most familiar b/c part of every cell in

human body) Vitamin D Steroid hormones

Categories of Lipids

Based on Molecular Structure

Based on Physical State

Based on Dietary Sources

Categories Based on Molecular Structure

Saturated: when fatty acids have the maximum number of hydrogen atoms. Butyric: Stearic:

Unsaturated: when fatty acid does not contain all the hydrogen atoms it could contain.

Monounsaturated: fatty acids that have 1 double bond in the carbon chain. Oleic: Erucic:

Polyunsaturated: Fatty acids have 2 or more double bonds in the carbon chain. Linoleic: Linolenic:

See page 273 in textbook

What are Trans Fatty Acids?

See page 278 in textbook

Categories Based on Physical State

One of the easiest ways to categorize lipids is by their physical state at room temperature.

Fats: lipids are solid at room temp. Oils: lipids are liquid at room temp. The #’s of hydrogen and carbon atoms on a fatty

acid chain determine the temp. at which lipids liquefy. More hydrogen = higher melting point More double bonds = lower melting point

The type of fatty acid present in the largest amount has has greatest effect on characteristics of the lipid. (see page 277 in textbook)

Categories Based on Physical State

Melting point: temp. at which a substance changes from solid to liquid.

Hydrogenated Vegetable Oils Hydrogenation: the process of adding hydrogen

atoms to an unsaturated lipid to increase its saturation level. Used to make oils solid at room temp

▪ Ex : margerine Achieved by bubbling hydrogen through liquid oil in the

presence of a nickel catalyst. Advantages include:

Longer shelf life than oil or lard Greater stability than lard Lower production cost than lard Faster dissolving and setting properties in chocolate production.

Categories Based on Dietary Sources

Triglycerides come from 7 main groups of dietary sources.

Milkfats:

Lauric Acids:

Vegetable Butters:

Oleic-linoleic acids:

Linolenic acid:

Animal Fats:

Marine Oils:

Physical Characteristics of

LipidsDiffering Melting and Solidification Points

Nonpolar Molecules

Tendency to Deteriorate

Differing Melting and Solidification Points

Lipids do not have a specific melting point because most lipids are mixtures of different fatty acids.

Lipids will also become solids at different temps.

Solidification point: the temp. at which all lipids in a mixture are in a solid state.

Nonpolar Molecules

Lipid molecules have a equal or balanced sharing of electrons, which makes them nonpolar.

Nonpolar molecules readily mix with other nonpolar molecules but do not want to mix with polar molecules This is why water and oil do not mix.

Lipids are large molecules with spaces between the parts of the molecules. This causes lipids to be less dense than water.▪ Ex: oil floats on water

Tendency to Deteriorate Lipids have a tendency to react with oxygen.Auto-oxidization: complex chain reaction

that starts when lipids are exposed to oxygen. Oxygen will bind to the lipid molecules and then to

other compounds. (domino effect) Starts to form other compounds and makes food

rancid (bad flavor, color, and odor)Antioxidants: compounds that quickly react

with oxygen to form new substances. Will react with oxygen before lipids do.▪ Ex: vitamins A,C, and E.

Functions of Lipids in Food Preparation

Transfer HeatTenderizeAerateEnhance FlavorLubricateServe as Liquids in Emulsions

Transfer Heat

Excellent heat medium Temp. of lipids will continue to

increase as heat is added. Every lipid has a temp. at which the

fatty acids begin to break apart and produce smoke. This temp. is called the smoke point.

Once oil starts to smoke, nothing should be cooked in it, or it should be discarded, because it will cause an unpleasant flavor.

Transfer Heat

Flash point is the temperature at which lipids will flame (this occurs around 600 degrees F).

Do not salt food until after deep frying because it will lower the smoke point of the oil, reducing the time the oil can be used.

Tenderize Tenderize baked goods Protein in baked goods have long strands

and the lipids tend to shorten those strands. That is why the solid white fate sold for baking is

called shortening. Fat to flour ratio will determine how flaky a

baked product. You cut in fats to dry ingredients and do

not over mix or the dough will not be suitable for baked goods. Will become a greasy ball

Tenderize

Aerate The addition of air into a batter. Saturated fats allow tiny air

pockets to form when batters are sufficiently beaten.

Oils are not suitable for this because they will separate from the mixture.

In cakes: You cream the ingredients together

to aerate them. You cant heat them too high because you don’t want them to melt (then they act like oils).

Enhance Flavor

Fat is a major flavor enhancer. Overeaten by most people in the

U.S. Used in preparation of many foods:

Salad dressings, sauces, soups, casseroles, etc.

When you want to taste more of the main food product and not the fat, use oils that have very little taste Ex: soybean oil, canola oil, and

sunflower oil.

Lubricate

Makes meat easier to chew as the fat content increases.

Pleasant mouth feel Feel slick or smooth to the tongue Foods seem moister

Serve as Liquids in Emulsions

An emulsion is a mixture that contains a non-polar lipid and a water-based liquid, which is polar.

Another compound with a polar and nonpolar end must be added to emulsify

Phospholipids have this chemical structure and create emulsions. Ex: mayo, phospholipid (lecithin) fount in

egg yolks, prevents oil from separating.

Carbohydrates Versus Fats

Which is more fattening, 100 kilocalories of carbohydrates or 100 kilocalories of fat?

See page

289 in textbo

ok

Lipids in Your Diet

Functions of Lipids in the BodyEssential Fatty AcidsThe Role of CholesterolUnsaturated OilsDietary Recommendations

Functions of Lipids in the Body

Essential Fatty Acids

The Role of Cholesterol

Unsaturated Oils

Dietary Recommendations

Math Matters

Calorie DensitySee page 293 in textbook